Alan H. Harris

Instrumental Conditioning of Large-Magnitude, Daily, 12-Hour Blood Pressure Elevations in the Baboon

Blood pressure and heart rate were monitored continuously in four baboons during extended exposure to a daily 12-hour conditioning procedure providing food and shock-avoidance as contingent consequences of prespecified increases in diastolic blood pressure. Sustained and significant increases (30 to 40 mm-Hg) in both systolic and diastolic blood pressure were maintained throughout the daily 12-hour conditioning sessions, accompanied by elevated heart rates.

Novel long-term cardiovascular effects of industrial noise.

Baboon subjects were instrumented with indwelling arterial catheters for continuous measurement of blood pressure and heart rate before, during, and after exposure to industrial noise eight hours daily. Initial exposure to noise produced transient, acute elevations of systolic and diastolic blood pressures and heart rates at noise onset, which habituated over the course of noise exposure. Chronic exposure to noise lowered blood pressure and heart rate not only during noise, but particularly after daily noise offset. Blood pressures returned toward baseline after noise exposure was terminated. Plasma catecholamines were also decreased during noise exposure. A control animal which received only masking noise did not demonstrate decreases in cardiovascular parameters. The possibility of classically conditioned associations of noise onset with feeding was discussed.

Baroreflex sensitivity during operant blood pressure conditioning.

Baroreflex sensitivity was measured in baboons operantly conditioned to increase their diastolic blood pressure in daily, 12-hr sessions, by using the extent of increases in interpulse interval per unit of increase in systolic pressure after intravenous phenylephrine injection as an index of baroreflex sensitivity. Following training, baroreflex sensitivity increases averaging 32% were observed before and after the 12-hr conditioning sessions. During the conditioning sessions, however, consistent diastolic blood pressure elevations averaging 17% (14 mmHg) were accompanied by significant decreases in baroreflex sensitivity averaging 44% relative to the increased “before” and “after” sensitivity levels. The results suggest that changes in baroreflex sensitivity participate in operantly conditioned blood pressure changes.

Pure tone thresholds in the yellow baboon (Papio cynocephalus)

Abstract Using a reaction-time procedure, pure tone thresholds were measured behaviorally in four baboons at 12 frequencies, ranging from 62 Hz to 40 kHz. Lowest mean individual thresholds were in the range of 3 to -8 dB SPL between 1.0 and 16.0 kHz, and rose to 48 dB at 62 Hz, and 59 dB at 40.0 kHz. These threshold functions closely match those of other Old World monkeys.

Generalization of conditioned blood pressure elevations: Schedule and stimulus control effects

Abstract By using a combination of food-reward, shock-avoidance, and visual biofeedback, all contingent upon diastolic blood pressure, baboons were conditioned, in 3–4 months, to raise their blood pressure 30–50% (25–40 mmHg) above preconditioning baseline levels, and maintain the increased pressure during daily 12-hr training sessions. Under conditions where exteroceptive stimuli reliably predict environment events, animals appear to learn to stop making the blood pressure increase response when discriminative periods of safety are in effect within sessions and when training sessions are over. By gradually eliminating feedback, withholding food rewards, and punishing short-term falls in diastolic pressure, elevations in blood pressure were maintained continuously during training sessions and for periods up to 2 hr following the offset of training sessions.

Performance characteristics of conditioned blood pressure elevations in the baboon.

Operant conditioning of diastolic blood pressure elevation was accomplished in six baboons (Papio sp.) by a procedure using food delivery when diastolic pressure was maintained above a prespecified level, and shock delivery when diastolic pressure remained below that level. Data from steady-state performance indicated a rise in diastolic pressure by a median 22 mm Hg when the daily session was begun. Elevated levels of diastolic blood pressure and low shock frequencies were maintained throughout the 12-hour session. The frequency and duration of shifts in diastolic pressure to below criterion level were found to be variable during the first 1–2 hours but were stable throughout the remainder of the session. Heart rate had a phasic temporal pattern over the 12-hour session, characterized for most subjects by a rate increase at session onset followed by a rate decrease. Analysis of individual performance records showed that the blood pressure increases could occur without concomitant elevations in heart rate.

Plasma lactate levels during baseline and blood pressure conditioning in the baboon

Lactic acid in arterial blood, systolic and diastolic blood pressures, and heart rates of baboons were examined for three naive subjects, and for five experimental subjects during baseline conditions and during training to elevate diastolic blood pressure through operant conditioning methodology. Lactic acid and cardiovascular levels were determined at rest (9 a.m.), and at 12:30 and 3:00 p.m. (during conditioning sessions, for trained subjects). At rest (baseline) lactic acid levels and cardiovascular measures were similar for conditioned and naive subjects. During conditioning sessions, blood pressures but not heart rates were significantly elevated. Plasma lactate increased from morning to afternoon in both naive and trained subjects, but at three hours of conditioning, trained subjects had significantly higher lactate levels than when at rest and when compared to naive subjects at the same time of day. This study provides normative data for plasma lactate in the laboratory baboon and also indicates metabolic changes (which may be related to increased muscular work) as part of concurrent changes in multiple systems (e.g., neural, hormonal) which accompany conditioned blood pressure elevations.

Instrumental conditioning of blood pressure elevations in the baboon

Two adult male baboons were surgically prepared with arterial catheters which provided a continuous measure of blood pressure and heart rate. Environmental consequences (food and electric shock) were made contingent upon prespecified increases in diastolic blood pressure levels. Continued exposure to these contingencies resulted in substantial increases in both diastolic and systolic pressures. The results demonstrated that blood pressure changes are highly susceptible to both operant“shaping” and stimulus control procedures and extend the range of instrumental conditioning effects upon the cardiovascular system.

Sympathetic adrenergic blockade effects upon operantly conditioned blood pressure elevations in baboons.

Sympathetic adrenergic nervous activity during operantly conditioned hypertension was evaluated by assessing the effects of specific alpha-(phentolamine or phenoxybenzamine) and beta- (propranolol) adrenergic blockers in baboons reinforced for increasing diastolic pressure in daily, 12-h sessions. In the first 10 min of control (no blockade) sessions, mean heart rate increased 24 bpm (21%) above the value for the 10 min immediately prior to the beginning of the sessions; systolic pressure increased 27 mm Hg (22%) and diastolic pressure increased 24 mm Hg (31%). Betablockade eliminated the tachycardia but did not attenuate the increased blood pressure. Alpha-blockade did not attenuate the increased blood pressure significantly either. Combined alpha- and beta-blockade did significantly attenuate the increase in diastolic pressure, but consistent, significant increases in systolic pressure (17 mm Hg, 17%) and diastolic pressure (16 mm Hg, 26%) still occurred. The results support the participation of the sympathetic adrenergic nervous system in producing operantly conditioned blood pressure changes, but the results are also consistent with the additional participation of nonadrenergic factors in operantly conditioned hypertension.

Operant Conditioning of Large Magnitude, 12-hour Duration, Heart Rate Elevations in the Baboon

Two baboons were prepared with arterial and venous catheters and their heart rate and blood pressure were monitored continuously thereafter. Following a 2 to 3 week interval during which baseline cardiovascular levels were determined, the animals were exposed to daily 12 hr conditioning sessions (alternating with 12-hr “rest” or “Conditioning Off’ sessions) during which food reward and shockavoidance were programmed as contingent consequences of pre-specified increases in heart rate. Initially, the criterion heart rate was set at 10–15 bpm above the animal’s pre-experimental resting baseline level, with progressive increases programmed to occur at a rate approximating 7 bpm per week over a period of 8–10 weeks. Within this 2–3 month interval, heart rate doubled, reaching levels maintained above 160 bpm for more than 95 per cent of each daily 12-hour “Conditioning On” period. Propranolol selectively eliminated the conditioned heart rate increase but not the blood pressure elevation, indicating the contribution of sympathetic nervous activity to these operantly conditioned cardiovascular changes.